1. Bozeman Osmoregulation - 197

2. Excretory System and Osmoregulation
Posterior vena cava
Renal artery and vein
Aorta
Ureter
Urinary bladder
Urethra
(a) Excretory organs and major
associated blood vessels
Kidney
Excretory System and Osmoregulation
Chapter 44
199

3. Osmoregulation
The regulating of water and solute concentrations to maintain homeostasis
Osmolarity – moles solute / liter
Isoosmotic – equal osmolarity internal and external
Hypoosmotic – more dilute = more H2O
Hyperosmotic – more concentrated = less H2O more solute

4. Osmoregulation
Osmoconformers – isoosmotic with external environment and therefore do not need to regulate osmolarity
Marine invertebrates
Osmoregulators – body fluids are not isoosmotic with external environment
Environment
Hypoosmotic – water constantly diffuses into the organism and they must get rid of excess water
Freshwater animals and fish – constantly peeing
Hyperosmotic – water constantly diffuses from the organism and they must uptake water
Marine fish – drink saltwater to take in water and actively pump out the salt

5. Osmoregulation Freshwater Marine Uptake of water and some ions in food
Osmotic water gain
through gills and other parts
of body surface
salt ions
by gills
Excretion of
large amounts of
water in dilute
urine from kidneys
Gain of water and
salt ions from food
and by drinking
seawater
Osmotic water loss
through gills and other parts
of body surface
Excretion of
salt ions
from gills
Excretion of salt ions
and small amounts
of water in scanty
urine from kidneys

6. Excretory System - 199 Functions
Rid the body of nitrogen containing waste
Rid the body of metabolic wastes
Maintain homeostasis
Filtration
Reabsorption
Secretion
Excretion
Filtration. The excretory tubule collects a filtrate from the blood.
Water and solutes are forced by blood pressure across the
selectively permeable membranes of a cluster of capillaries and
into the excretory tubule.
Reabsorption. The transport epithelium reclaims valuable substances
from the filtrate and returns them to the body fluids.
Secretion. Other substances, such as toxins and excess ions, are
extracted from body fluids and added to the contents of the excretory
tubule.
Excretion. The filtrate leaves the system and the body.
Capillary
Excretory
tubule
Filtrate
Urine 1 2 3 4

7. Excretory System Structures Lungs Renal artery Skin Renal vein Kidney
Renal cortex
Renal medulla
Nephrons
Renal artery
Renal vein
Ureter
Urinary bladder
Urethra

8. 198
IQ 44.5
Structure your knowledge #1

9. Juxta- medullary nephron Cortical To renal pelvis Renal cortex medulla
Collecting
duct To
renal
pelvis
Renal
cortex
medulla
20 µm
Afferent
arteriole
from renal
artery
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
SEM
Efferent
arteriole from
glomerulus
Branch of
renal vein
Descending
limb
Ascending
Loop of
Henle
Distal
tubule
(c) Nephron
Vasa recta
(d) Filtrate and
blood flow

10. Nitrogenous waste disposal - 201
Ammonia – highly toxic
Requires lots of water to excrete
Freshwater fish
Urea – less toxic
Requires minimal water
Requires energy to convert from ammonia
Land animals and marine fish
Uric Acid – virtually nontoxic
Insoluble in water – paste
Extremely energetically costly to produce
Reptiles and birds – low access to water

11. Proteins
Nucleic acids
Amino acids
Nitrogenous bases
–NH2
Amino groups
Most aquatic
animals, including
most bony fishes
Mammals, most
amphibians, sharks,
some bony fishes
Many reptiles
(including
birds), insects,
land snails
Ammonia
Urea
Uric acid
NH3
NH2 O C N H HN

12. Filtration - 201
Blood is first filtered in the liver removing toxins to produce urea which travels to the kidney.
Blood pressure forces blood in the glomerulus into the Bowman’s capsule
Water and small solutes pass through the Bowman’s capsule and large molecules such as blood cells and proteins stay in the capillaries
Filtrate

13. Reabsorption
Valuable substances in the filtrate are reabsorbed into the capillaries of the blood.
Proximal (convoluted) tubule
Loop of Henle
Distal (convoluted) tubule
Collecting Duct

14. Secretion
Transfer of substances such as toxins from the blood in the capillaries to the Nephron (renal tubule)
Maintains the pH of blood
PCT and DCT H+
NH3

15. Proximal tubule
Filtrate
H2O
Salts (NaCl and others)
HCO3– H+
Urea
Glucose; amino acids
Some drugs
Key
Active transport
Passive transport
CORTEX
OUTER
MEDULLA
INNER
Descending limb
of loop of
Henle
Thick segment
of ascending
limb
Thin segment
Collecting
duct
NaCl
Distal tubule
Nutrients
HCO3 K+
NH3 1 4 3 2 5

16. Osmolarity of interstitial fluid (mosm/L)
H2O
NaCl
300
100
400
600
900
1200
700
200
Active transport
Passive transport
OUTER MEDULLA
INNER MEDULLA
CORTEX
Urea
Osmolarity of interstitial fluid (mosm/L)

17. Section of kidney from a rat
Excretion
Collecting Duct
Carries filtrate (urine) from multiple nephrons to the renal pelvis to the ureter to the bladder to the urethra where it is excreted.
(b) Kidney structure
Ureter
Section of kidney from a rat
Renal
medulla
cortex
pelvis

18. Flow map – Excretion of nitrogenous wastes – start in the liver
Summarize

19. Feedback mechanisms – 205 -209